Strategies currently used to produce hybrid solar cell devices are limited, in part because they typically produce organic domains that are too large (typically >50 nm). This large size results in significant exciton decay before diffusion to p/n interface can occur. Despite currently having very low efficiency values, hybrid solar cells could prove to be one of the most disruptive technologies in the solar-module market because of (1) their very low production cost, (2) their potential for long-term stability and (3) their great potential for producing high efficiency multi-junction devices.
Typically, in the above methodology, a porous inorganic framework is synthesized using a variety of methods and it is subsequently filled, or at least partially filled, with suitable organic components. Unfortunately, inorganic frameworks cannot be produced with pores smaller than typical values for the exciton diffusion length (<10 nm). Furthermore, even if these small pore structures could be fabricated, diffusion and viscous limitations become increasingly severe and block the infiltration of the organic material.
The efficiency of previous hybrid cells has remained disappointingly low and improvements have been incremental and slow. This stark lack of progress originates from a fundamental flaw in the way hybrid devices are produced.
Some current approaches to generating hybrid photovoltaics include templated growth of zinc oxide (ZnO) nanowires and subsequent backfilling with poly(3-hexylthiophene) (P3HT). Devices based on this approach have limited applications because of the templating process and, moreover suffer from poor interfacial contact between materials with reported optimized power conversion efficiencies (PCE) of 2.7% or less. Another reported approach included the mixing of P3HT and ZnO nanoparticles in a single solution for coating from solution. While this approach is not limited by processability, it is limited by the random morphology of the photoactive layer that limits phase interconnectivity and, therefore, has resulted in reported optimized PCE of 2.0% or less.